1. Field of the Invention
The present invention relates to an apparatus for predicting reliability in an electronic device package, a program for predicting reliability in an electronic device package, and a method for predicting reliability in an electronic device package, at the stage of designing the electronic device package.
2. Description of the Related Art
In electronic equipment represented by a personal computer, a portable cellular phone, and the like, various electronic components have become more and more integrated and have a high density. In connection with this, the pitch of terminals disposed in an electronic device package, including these electronic components and incorporated in the electronic equipment, (i.e., a distance between adjoining terminals) has become smaller. As these electronic components mounted in an electronic device package are more and more integrated with high density (i.e., the electronic device package is designed to be very compact), reliability in the mounted electronic components and, more particularly, reliability at a solder joint, has become very important. In order to mount numerous electronic components in the electronic device package with high density, a ball grid array (BGA) package (that is, a kind of surface mounting package in which spherical solder-balls are arranged in the form of array on the rear surface of a printed-circuit board, without using lead terminals) or a chip size package (CSP) (that is, an large-scale integrated (LSI) package having substantially the same dimensions as a chip) has become widely adopted. A solder joint included in the electronic device package, the BGA package, the CSP, or the like, for an electronic device is normally called as a “micro-joint.” The solder joint in the above electronic device package is subjected to stresses including a variation in temperature, an impact caused by a drop, and the like. When an attempt is made to apply the solder joint to an actual product, reliability in the strength of the entire electronic device package including the solder joint must be assessed satisfactorily.
One typical method for assessing the strength of a micro-joint in an electronic device package includes an assessment method that utilizes a computer aided engineering (CAE) (more specifically, a numerical analysis and a simulation that is to be carried out by a computer in the course of designing or developing an industrial product) system on the basis of a simulation technology, such as an analysis by a finite element method (FEM simulation). In designing or developing a new electronic device package, it has now become a conventional technique to use a CAE system for assessing the above strength. However, the structure of the electronic device package is so complex that it takes much time to create a simulation model or carry out the calculations required for a simulation. Furthermore, for example, when a simulation model for a solder joint is to be created, the material that is to be used for forming the solder joint is liable to be non-linearly deformed, owing to creep deformation, etc. Therefore, it is difficult to obtain appropriate data concerning material properties. Furthermore, the setting for the simulation is complex, and therefore, it is necessary to have specialized knowledge about various program codes, including a specific program code for carrying out the finite element method. Because of the above-mentioned problems, it is difficult for an ordinary designer, a factory worker, or a responsible person who needs most earnestly information about the strength of the solder joint, to make an assessment by directly carrying out the simulation.
Further, the assessment of the results of simulation also causes the following problem. When the simulation is carried out in order to assess a solder joint or the like, as the place in which a maximum stress or a maximum strain occurs is the end portion of a joint interface between solder and any material other than solder, the end portion of the joint interface is regarded as a stress singularity place. Depending on the method for creating a simulation model, the value of the maximum stress or maximum strain varies greatly. In other words, specialized knowledges about both a modeling method for creating the simulation model and the assessment of the results of simulation obtained actually by carrying out the simulation are needed.
On the other hand, when a simulation is carried out in order to assess the strength of an entire electronic device package, namely, when the simulation is carried out in order to simultaneously assess both a microscopic joint such as a micro-joint and the entire electronic device package, the size of a simulation model is relatively large. It therefore takes much time to carry out simulation-related calculations. In particular, there are some kinds of simulations in which several days may be required in order to obtain the required results of simulation. This hinders the rapid and accurate assessment and causes the delay in design changes.
For example, as described in Japanese Unexamined Patent Publication (Kokai) No. 2000-304630 (hereinafter referred to as Patent Document No. 1) and Japanese Unexamined Patent Publication (Kokai) No. 2000-99550 (hereinafter referred to as Patent Document No. 2), various techniques have been devised as the related art in efforts to speed up a simulation that to be carried out in order to assess the strength, etc., of an entire electronic device package.
Patent Document No. 1 discloses a method, for analyzing a mounted semiconductor device package, in which a structure model having a BGA package or a CSP mounted on a printed-circuit board is used to rapidly and highly accurately analyze a simulation that is carried out in order to assess a thermal strain generated in a solder joint and the prediction of a service life of the solder joint. In the method for analyzing the semiconductor device package mounted structure, a two-dimensional planar model is normally used to carry out the simulation. Thus, the service life of the solder joint in an electronic device package can be predicted. A technology for predicting the service life by means of an analysis by using a normal two-dimensional planar model is already widely known. In Patent Document No. 1, a parameter representing a thickness direction and being designated an analysis for the two-dimensional planar model is adjusted to be consistent with an actual phenomenon.
Patent Document No. 2 discloses a method for analyzing an IC package. In this method, when a service life of an electronic device package is predicted by means of a three-dimensional analysis, a coarse model is used to schematically analyze an analytic model for the three-dimensional analysis, in advance of highly accurately and efficiently carrying out three-dimensional analysis. A region of interest is determined by schematically analyzing the analytic model, and subsequently, a detailed model is created. Consequently, highly accurate analysis of the IC package can be carried out by analyzing the detailed model.
However, when a CAE system based on a simulation technology such as an analysis by a finite element method or the like is used to generally assess an electronic device package according to a conventional method described in Patent Document No. 1 or No. 2, the following problems occur. It is difficult to obtain data concerning material properties (i.e., material property values), it is difficult to create an analytic model because of the complex structure of the electronic device package, and it takes much time to carry out a simulation. Further, it is almost impossible for a person having no specialized knowledge to make assessment directly by carrying out the simulation.